Jonny Wilkinson was approached by the Lions but turned down the opportunity to go on the tour to Australia due to fitness reasons and his club commitments, Warren Gatland has revealed.

Speaking after naming his 37-man squad for this summer's tour to Australia, the British and Irish Lions head coach said that he had called Wilkinson on Monday to "sound him out", but the 2003 World Cup winner said that he was committed to helping Toulon attempt to win a Heineken Cup and Top 14 double.

The tour manager, Andy Irvine, then added on Radio 5 Live: "The truth is Jonny wasn't up for it. He ruled himself out. He told Warren that he feels his body isn't in the right shape to complete a tour like this. I admire his honesty and integrity. He could be available as injury replacement."

Gatland had promised surprises but the Lions head coach came up with shocks as he successfully prevented his squad from leaking out prematurely: no utility back, which will mean a lack of specialist cover at outside-half in the midweek matches before the first two Tests, the selection of Matt Stevens as one of the props a year after he retired from Test rugby and the preference for Dylan Hartley at hooker rather than Ireland's Rory Best among them.

Hartley's inclusion and the lack of a playmaker are more than a hint about how Gatland sees the series being won. The Lions management paid tribute to the running game of Australia, all angles and sleight of hand, and their ability to create tries but the lines they will be running will be straight and by focusing on the scrum and breakdown, they are aiming to starve the Wallaby backs.

Gatland publicly identified Hartley as a weak link before Wales played England in 2011, goading the New Zealander about a suspected volatility only for the grenade to blow up in his hand. Hartley served a ban earlier this season after being cited for whacking Best off the ball in a Heineken Cup match between Northampton and Ulster and his aggressive competitiveness will ensure sparky training sessions.

Wilkinson would have fitted in well, but the lack of a third fly-half worked against the Toulon No10 who, depending on how his club do in the Top 14 play-offs, may not have been available for the first two matches and there was a question mark over his fitness; he may need knee surgery. Owen Farrell and Jonathan Sexton are the two 10s and the cover will be provided by Stuart Hogg, the Scotland full-back who played at stand-off in school.

None of the four centres picked can be described as a second-five: Jamie Roberts is the only one of the quartet who played for his country at 12, Jonathan Davies, Brian O'Driscoll and Manu Tuilagi all 13s, and the early midfield combinations will be instructive. O'Driscoll will be tried out at inside-centre early on.

Similarly, three of the four wings prefer playing on the right, Scotland's Sean Maitland gaining selection despite not being one of the 50 players who received a letter earlier this year asking about their availability. Gatland said some positions were not decided until the seventh meeting of the coaches on Monday night: Mako Vunipola did enough for Saracens against Toulon to join Cian Healy and Gethin Jenkins as the looseheads, while Stevens profited from Mike Ross and Euan Murray being considered one-dimensional tightheads.

Omissions often attract more media attention than selections when it comes to the Lions, but Chris Robshaw had long been flagged up as a possible rather than a probable. It was the position of greatest strength for the Lions and the return to fitness of Dan Lydiate did for the England captain, who was seen by the Lions as a 6, not a 7, where the tour captain Sam Warburton will face competition from his compatriot, Justin Tipuric.

Gatland said he named Warburton, who led Wales only once in the Six Nations, as his captain because he was the most successful Test captain in the four home unions in recent years, but the flanker has yet to lead his country to success against Australia in six attempts, matches in which Wales have opted for power but not finesse.

Nearly one-third of the squad has been on at least one previous Lions tour. All the backs are first choices for their country, while at forward, Hartley was on England's bench for most of the Six Nations having missed the autumn internationals through injury, Stevens is now a club player and Wales will next season have to decide between Warburton, Tipuric and Lydiate for the flanker berths.

The management are a mix of England and Wales and 25 of the 37 players picked are from the Six Nations' winners and runners-up. The Lions stressed that with so little time to prepare for the tour it was essential to have working combinations, as they have in all areas of the back division and most of the three rows at forward.

Every player will start one of the first three matches. Gethin Jenkins is the only player chosen who is based in France: the Lions hope he will be released early by Toulon and while the standby list of players will not be revealed publicly, it will not contain many players who are based in the Top 14.